<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <style>
        .demo2 span {
            width: 200px;
            height: 200px;
            background-color: red;
        }
    </style>
    <div class="demo2">
        <span>child1</span>
        <span>child2</span>
        <span>child3</span>
    </div>
</body>

</html>